1. Field of the Invention
The present invention relates to monitoring apparatuses and more particularly to a method of monitoring the electric power, that is, the condition of a battery by measuring the internal resistance of the battery by means of an external load and comparing the internal resistance of the battery with a predetermined warning value thereof so as to display a warning if the power is lower than a predetermined level.
2. Description of Related Art
It is known that a driver has to start the engine of a motor vehicle prior to driving it. Also, for successfully starting the engine, there must be sufficient electric power in the battery. Typically, a battery has an approximate lifetime. However, factors such as ambient temperature, charging conditions and time, and load discharge all can adversely affect the lifetime of the battery. Thus, there is a difference between the practical lifetime and the design lifetime of any particular battery and the difference is sometimes very large. Hence, in practice, there is no way for a driver (even an experienced one) to know the electric power level of the battery prior to starting the engine. Typically, only a motor vehicle repair shop can know the electric power level by means of a measuring device. The measuring device is bulky, thus prohibiting it from being carried by the motor vehicle. It is common that a driver finds the battery to be low only when it fails to start the engine. Alternatively, the battery may be already damaged but the driver is not aware before a next start even it is successful in a particular start. This is not desirable and may even be dangerous since the driver may park his/her car in a remote area, mountain, or desert.
Advantageously, a battery power measuring device would be installed in a car as a requisite equipment. But power measurement of the battery may also consume the electric power of the battery. Hence, a frequent power measurement is not desirable. Thus, it is desirable to accurately measure the electric power of battery in a relatively short period of time by consuming a minimum electric power thereof. The present application is relevant to commonly assigned U.S. Pat. Nos. 6,704,629 and 6,791,464, both entitled “Device for Monitoring Motor Vehicle's Electric Power and Method Thereof”, both incorporated by reference herein.